In recent years, silicon carbide single crystal substrates have been adopted as semiconductor substrates for use in manufacturing semiconductor devices. Silicon carbide has a band gap larger than that of silicon, which has been used more commonly in the field of semiconductor. Hence, a semiconductor device employing silicon carbide advantageously has a large reverse breakdown voltage, low on-resistance, and has properties less likely to decrease in a high temperature environment.
A silicon carbide single crystal is manufactured using a sublimation-recrystallization method. Specifically, a silicon carbide single crystal is grown on a surface of a seed crystal fixed on a pedestal. If the seed crystal is not uniformly fixed on the pedestal, the single crystal grown on the seed crystal may have a reduced quality. Thus, as a method of mounting the seed crystal to the pedestal, for example, the following two methods have been proposed.
Firstly, according to Japanese Patent Laying-Open No. 2001-139394 (Patent Literature 1), when a single crystal is grown, a carbon composite structure having graphite fine particles and non-graphitizable carbon is formed in an interface between a seed crystal and a seed crystal pedestal. This publication describes that, since carbon is thereby uniformly formed all over an attachment surface using heat-resistant fine particles uniformly dispersed in the attachment surface as cores, and covers an attachment surface of the seed crystal, it is possible to prevent occurrence of recrystallization in the attachment surface of the seed crystal to be attached to the pedestal during growth of the single crystal, and it is also possible to prevent etching which may occur at a central portion of the seed crystal in an early stage of the growth.
Secondly, according to Japanese Patent Laying-Open No. 2003-226600 (Patent Literature 2), a silicon carbide seed crystal having a protective film with a thickness of 0.5 to 5 μm formed on a backside surface thereof is mechanically mounted on a graphite crucible lid. This publication describes that, since the protective film can prevent sublimation of Si atoms from the backside surface of the seed crystal, generation of voids in a crystal is suppressed.